This guide worked 100% for me - it takes you through each step. Afterwards, the m4a file plays! Note: this is completely free. http://sysfrontier.com/en/2014/12/31/hello-world/
Also pasting instructions in case the link goes down in future:
How to fix corrupted voice memo (m4a) files.
Do you have broken voice memo files? You can fix those files by
The right way to do this is open the project in GarageBand and export each track as its own audio file. Then you can import the audio files into a PC-based multichannel audio editor and continue working.
Failing that, though, notice that the GarageBand project is a folder, and inside the folder there is a “Media” folder that contains the individual audio ...
You could try rewriting the file using ffmpeg with the following command:
ffmpeg -i damagedfile.mp4 -c copy fixedfile.aac
Alternatively you may use FAAD and a hex editor (e.g. Hexplorer). Find out where the actual data starts in a hex editor. Not always after the mdat entry - there may be alot of zeros in the beginning of the file.
Simply copy everything ...
Ogg Vorbis doesn't suffer from much of the horriffic issues that occur with MP3, and generally produces smaller files.
Hi Quality Voice Recorder will do what you want.
If you need smaller, obviously gsm which is the encoding used for mobile phone calls should be suffficient, but there is less software compatible with this format.
From this wikipedia article:
Unlike a WAV file, a VOX file does not contain a header to specify the
encoding format or the sampling rate, so this information must be
known in order to play the file. If not known, it is normally assumed
that a VOX file is encoded with Dialogic ADPCM at a sampling rate of
8000 Hz. It is possible that a VOX file may ...
I've had this happen before, howevr it was while recording the screen of my computer. Not certain if you've done the same or used a camera IRL. However easiest way to see if there's audio in a file is to play the file in VLC and press CMD+I or CTRL+I (Window>Media Information)
Notice under CODEC Details "Stream 0" & "Stream 1". 0 is your video and 1 is ...
Try opening the file with some advanced video players just to find out if the audio is gone or there's a codec error.
Two video players that I use when having this sort of problems is Quick Time and Video Lan.
If indeed there's no audio attached to the video - there's little to be done - maybe useing a disk data recovery tool depending on the recording ...
Just an idea (which needs further research): do you actually need the silence to be a file or could you just play dynamically created data? If the latter is the case, you could probably find a solution to call a program that creates a silent audio file in realtime and put that in your playlist. That way you would entirely get around the file size issues for ...
If you're just taking existing songs (mp3's for example) you could sort of have each "section" of the orchestra segregated by their main frequency bands and just increase/decrease those frequencies. wouldn't be great. Ideally you'd have multitracks of each section. There's a nice resource of multitrack audio at cambridge-mt.com, but not a lot of ...
you can go for things like "Soundfonts" and apply them on "midi" files but there is no other format for getting pre-recorded "audio" instrument tracks separately. I think Midi files could be enough to fit your needs.
if you choose "midi" format there are many many websites, just Google it. some examples: